Sirtuins are a class of enzymes known as nicotinamide adenine dinucleotide (NAD)-dependent deacetylases. Humans have seven sirtuins, Sirt1-7, that regulate a variety of biological processes, including aging, transcription, and metabolism. Therefore, small molecules that can regulate sirtuin activity can be used to treat several human diseases.
Of the seven human sirtuins, Sirt6 is of particular importance because of its roles in controlling metabolism and genome stability. The biological function of Sirt6 makes it a promising target to treat fatty liver diseases, obesity, and diabetes. Therefore, small molecules that can activate, inhibit, or otherwise modulate Sirt6 would be highly beneficial in treating such diseases and conditions.
The malaria parasite Plasmodium falciparum contains two sirtuins, PfSir2a and PfSir2b. These sirtuins are known to regulate the expression of virulence genes, antigenic variation, and antigenic gene expression, which helps the malaria parasite evade detection by the host's immune system. Thus, small molecules that can inhibit or otherwise beneficially modulate these sirtuins can be used in the treatment of malaria, which would also be highly beneficial.
The development of Sirt6 and PfSir2a inhibitors has been hampered by the lack of an effective activity assay for Sirt6 and PfSir2a, particularly one that can be used in a high-throughput manner. This difficulty in developing an effective activity assay for Sirt6 and PfSir2a is primarily a result of the very weak deacetylase activity of Sirt6 and PfSir2a. Among the seven mammalian sirtuins, Sirtuins 4-7 have either weak or no deacetylase activity. Sirt6 is known to function as a histone H3K9- and H3K56-specific deacetylase because other acetyl peptides cannot be hydrolyzed by Sirt6. However, the deacetylase activity is very weak and no kcat, and Km measurement has thus far been reported. Similarly, the deacetylase activity of PfSir2a is known to be much weaker than that of human Sirt1.